Inner peripheral surface shape of casing of axial-flow compressor

ABSTRACT

A generating line of a casing surrounding an outer periphery of vanes of a stator disposed downstream of a rotor of the axial-flow compressor includes: a recessed region recessed outward in a radial direction from a position forward of a front edge of each of the vanes to a position rearward of a rear edge of the vane; and a protruding region bulging inward in the radial direction at an intermediate position of the recessed region in a front-rear direction thereof. Thus, a distribution of static pressure in the radial direction on a surface of the vane is improved by a first recessed portion forward of the protruding region, and the static pressure on the tip side is raised by a second recessed portion rearward of the protruding region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inner peripheral surface shape of a casing of an axial-flow compressor, the casing surrounding an outer periphery of vanes of a stator which are disposed in a radial arrangement and downstream of a rotor of the axial-flow compressor.

2. Description of the Related Art

An inner peripheral surface (a peripheral surface on a tip side) of a fan casing surrounding an outer periphery of a fan stator of a turbofan engine is formed to have a substantially cylindrical shape having the center at the position of a shaft. In many cases, the shape of a generating line thereof (a line at which a plane passing the shaft crosses the inner peripheral surface of the fan casing) is a straight line. In addition, in some cases, stator vanes of the fan stator of the turbofan engine extend from a hub side to a tip side while being swept rearward (inclining rearward) so as to reduce shock-wave loss and reduce noises.

Japanese Patent Application Laid-open No. 2008-274926 describes a fan casing surrounding an outer periphery of inlet guide vanes (stator vanes) of a turbine. The fan casing has an inner peripheral surface a generating line of which is in a shape including outer peripheral protruding portions Cv2, Cv4 protruding inward in a radial direction on the upstream side and outer peripheral recessed portions Cc2, Cc4 recessed outward in the radial direction on the downstream side. With this shape, a secondary flow flowing inward in the radial direction, i.e., from the tip side to the hub side, can thus be suppressed to reduce pressure loss.

In addition, Japanese Patent Application Laid-open No. 7-247996 describes a casing surrounding an outer periphery of stator vanes of a compressor of a gas turbine engine. The casing has an inner peripheral surface a generating line of which is in a shape including a recessed portion 18 recessed outward in a radial direction. With this shape, the flow rate on the back surface side (on the suction surface side) of the stator vanes is reduced to prevent separation, and thus pressure loss is reduced.

Meanwhile, in the case of stator vanes of a fan stator each being swept rearward from the hub side to the tip side, particularly, a low-momentum fluid migration flowing from the hub side to the tip side along the surfaces of the stator vanes is accelerated, so that the pressure loss is increased. This acceleration is caused by the phenomena that the static pressure gradient in a peripheral direction, i.e., from the pressure surface side to the suction surface side of the stator vane near an end wall at the hub side increases at the rear part of the cascade, and that a static pressure contour extending from the hub side to the tip side on the suction surface of each stator vane is inclined against a mainstream.

SUMMARY OF THE INVENTION

The present invention has been made in view of the aforementioned circumstances. An object of the invention is to suppress a low-momentum fluid migration flowing from a hub side to a tip side of stator vanes of an axial-flow compressor and thus to reduce the pressure loss.

In order to achieve the object, according to a first feature of the present invention, there is provided an inner peripheral surface shape of a casing of an axial-flow compressor, the casing surrounding an outer periphery of vanes of a stator which are disposed in a radial arrangement and rearwardly of a rotor of the axial-flow compressor, wherein a generating line of the casing comprises a recessed region and a protruding region, the recessed region being recessed outward in a radial direction from a position frontwardly of a front edge of each of the vanes to a position rearwardly of a rear edge of the vane, the protruding region bulging inward in the radial direction at an intermediate position of the recessed region in a front-rear direction.

According to a second feature of the present invention, in addition to the first feature, there is provided the inner peripheral surface shape of a casing of an axial-flow compressor, wherein the recessed region comprises a first recessed portion on a front side, a second recessed portion on a rear side, a first protruding portion continuous to a front portion of the first recessed portion, a second protruding portion forming said protruding region, and a third protruding portion continuous to a rear portion of the second recessed portion.

According to a third feature of the present invention, in addition to the second feature, there is provided the inner peripheral surface shape of a casing of an axial-flow compressor, wherein the first protruding portion, the first recessed portion, the second protruding portion, the second recessed portion, and the third protruding portion are smoothly continuous to each other.

According to a fourth feature of the present invention, in addition to any one of the first to third features, there is provided the inner peripheral surface shape of a casing of an axial-flow compressor, wherein each of the vanes is swept so that a tip-side end portion thereof is positioned rearwardly of a hub-side end portion thereof.

According to the above features, the generating line of the casing surrounding the outer periphery of the vane of the stator disposed rearwardly of the rotor of the axial-flow compressor includes the recessed region and the protruding region, the recessed region being recessed outward in the radial direction from the position frontwardly of the front edge of the vane to the position rearwardly of the rear edge of the vane, the protruding region bulging inward in the radial direction at the intermediate position of the recessed region in the front-rear direction thereof. Accordingly, the distribution of the static pressure in the radial direction on the surface of the vane is improved by a part of the recessed region frontwardly of the protruding region, and the static pressure on the tip side is raised by a part of the recessed region rearwardly of the protruding region. Thereby, a low-momentum fluid migration flowing from the hub side to the tip side is suppressed, and thus the pressure loss can be reduced.

In addition, the recessed region includes the first recessed portion on the front side, the second recessed portion on the rear side, the first protruding portion continuous to the front portion of the first recessed portion, the second protruding portion forming the protruding region, and the third protruding portion continuous to the rear portion of the second recessed portion, and is continuous among them smoothly. This makes smooth an air flow along the inner peripheral surface of the casing.

Moreover, the vane is swept so that the tip-side end portion thereof is positioned rearwardly of the hub-side end portion thereof. Thus, the shock-wave loss can be reduced, and noises can be reduced. Although the sweep of the vane makes it easier for the low-momentum fluid to move from the hub-side end portion to the tip-side end portion, the low-momentum fluid migration can be effectively suppressed due to the inner peripheral surface shape of the casing of the present invention.

Note that a fan rotor 15 in an embodiment corresponds to the rotor of the present invention; a fan stator 16 in the embodiment corresponds to the stator of the present invention; stator vanes 23 in the embodiment correspond to the vanes of the present invention; and a second protruding portion 35 in the embodiment corresponds to the protruding region of the present invention.

The aforementioned and other objects, features, and advantages will be clear from a description to be given in detail below of a preferable embodiment with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 8 show the embodiment of the present invention:

FIG. 1 is a schematic view showing an overall configuration of a turbofan engine;

FIG. 2 is an enlarged view of a portion 2 in FIG. 1;

FIGS. 3A and 3B are sectional views taken along a line 3-3 in FIG. 2;

FIGS. 4A and 4B are views taken in directions of arrows 4A and 4B in FIGS. 3A and 3B, respectively;

FIGS. 5A and 5B are views showing wake states of stator vanes;

FIGS. 6A and 6B are views showing flow lines along suction surfaces of the stator vanes;

FIG. 7 is a graph showing changes of the total pressure loss involved with the change of the mass flow; and

FIG. 8 is a graph showing distribution of the total pressure loss of the stator vanes in a span direction.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A description is given below of an embodiment of the present invention with reference to the attached drawings.

Note that in this specification, an upstream side and a downstream side of an air flow direction are defined as “front” and “rear”, respectively, and an inner side in a radial direction and an outer side in the radial direction with an axis L being the center are defined as a hub side and a tip side, respectively.

As shown in FIG. 1, a turbofan engine E for an aircraft includes an outer casing 11 and an inner casing 12 which have substantially cylindrical shapes and are rotary bodies with an axis L being the center. Inside the outer casing 11 and the inner casing 12, a low-pressure shaft 13 and a high-pressure shaft 14 are coaxially arranged, the low-pressure shaft 13 being located on the axis L, the high-pressure shaft 14 being fitted around an outer periphery of the low-pressure shaft 13 in such a manner as to be freely and relatively rotatable.

A fan rotor 15 is provided at a front end of the low-pressure shaft 13, and a fan stator 16 is provided rearwardly of the fan rotor 15. A front portion of the outer casing 11 forms an outer portion 17A of a fan casing 17. The fan rotor 15 faces, on a tip side thereof, an inner peripheral surface of the outer portion 17A of the fan casing 17. In addition, the fan stator 16 is fixed, on the tip side thereof, to the inner peripheral surface of the outer portion 17A of the fan casing 17, while the fan stator 16 is fixed, on a hub side thereof, to an outer peripheral surface of an inner portion 17B of the fan casing 17.

A low-pressure compressor 18 is provided to the low-pressure shaft 13 rearwardly of the fan stator 16, and a low-pressure turbine 19 is provided to a rear end of the low-pressure shaft 13. In addition, a high-pressure compressor 20 facing a rear portion of the low-pressure compressor 18 is provided at a front end of the high-pressure shaft 14, and a high-pressure turbine 21 facing a front portion of the low-pressure turbine 19 is provided at a rear end of the high-pressure shaft 14. Further, multiple combustion chambers 22 are disposed between the high-pressure compressor 20 and the high-pressure turbine 21.

Thus, air compressed by the fan rotor 15 rotating together with the low-pressure shaft 13 is rectified by the fan stator 16. Thereafter, part of the air is exhausted rearward through a bypass duct 24 formed between the outer casing 11 and the inner casing 12. The remaining is supplied to the inside of the inner casing 12, compressed by the low-pressure compressor 18 rotating together with the low-pressure shaft 13 and by the high-pressure compressor 20 rotating together with the high-pressure shaft 14, and then mixed with fuel in the combustion chambers 22 to be supplied for combustion. The fuel gas exhausted from the combustion chambers 22 passes through the high-pressure turbine 21 to drive the high-pressure shaft 14, further passes through the low-pressure turbine 19 to drive the low-pressure shaft 13, and then is exhausted rearward from a rear end of the inner casing 12 to meet the air passing through the bypass duct 24.

FIG. 2 shows one of stator vanes 23 of the fan stator 16 disposed between the outer portion 17A and the inner portion 17B of the fan casing 17. In the stator vane 23, a hub-side end portion 23 c inward in a radial direction is connected to an outer peripheral surface of the inner portion 17B of the fan casing 17, and a tip-side end portion 23 d outward in the radial direction is connected to the inner peripheral surface of the outer portion 17A of the fan casing 17. A front edge 23 a and a rear edge 23 b of the stator vane 23 are swept in such a manner that the tip-side end portion 23 d deflects rearward relative to the hub-side end portion 23 c. Accordingly, a ¼ cord line 23 e of the stator vane 23 is also swept in such a manner that the tip side deflects rearward relative to the hub side. Thereby, an element in a cord direction of the flow rate of an air flow flowing along a surface of the stator vane 23 is reduced, and thus the critical Mach number is increased to delay an occurrence of a shock wave. Thus, the shock-wave loss can be reduced, and noises can be reduced.

The present invention is characterized by a shape, near the tip-side end portion 23 d of the stator vane 23, of the inner peripheral surface of the outer portion 17A of the fan casing 17. Since the fan casing 17 is basically a substantially cylindrical member which is a rotary body with the axis L being the center, a shape of an inner peripheral surface of the fan casing 17 is represented by a shape of a generating line (a line of intersection with a plane passing the axis L).

The shape of the generating line of the inner peripheral surface of the outer portion 17A of the fan casing 17 to which the tip-side end portion 23 d of the stator vane 23 is connected includes a recessed region 31 basically recessed outward in the radial direction from a position frontwardly of the front edge 23 a to a position rearwardly of the rear edge 23 b. The recessed region 31 includes a first recessed portion 32, a second recessed portion 33, a second protruding portion 35, a first protruding portion 34, and a third protruding portion 36. The first recessed portion 32 is located between a position slightly frontwardly of the front edge 23 a of the tip-side end portion 23 d of the stator vane 23 and a position slightly frontwardly of the rear edge 23 b thereof. The second recessed portion 33 is located rearwardly of the rear edge 23 b of the stator vane 23. The second protruding portion 35 bulges inward in the radial direction at a position slightly frontwardly of the rear edge 23 b in such a manner as to connect the first and second recessed portions 32, 33. The first protruding portion 34 connects a front end of the first recessed portion 32 to the inner peripheral surface of the outer portion 17A of the fan casing 17. The third protruding portion 36 connects a rear end of the second recessed portion 33 to the inner peripheral surface of the outer portion 17A of the fan casing 17. In other words, the recessed region 31 is formed by smoothly connecting the first protruding portion 34, the first recessed portion 32, the second protruding portion 35, the second recessed portion 33, and the third protruding portion 36 from the front to the rear. Positions of connecting points of the first protruding portion 34, the first recessed portion 32, the second protruding portion 35, the second recessed portion 33, and the third protruding portion 36 are inflexion points at which the direction of the curvature of the generating line changes.

Note that the dashed lines in FIG. 2 show the shapes of an inner peripheral surface of the fan casing 17 and an outer peripheral surface of the inner casing 12 in Comparative Example.

FIGS. 3A and 3B and FIGS. 4A and 4B show static pressure distributions around the stator vanes 23. FIGS. 3A and 3B show static pressure distributions on a cross section (of the tip-side end portion 23 d of the stator vane 23) taken along the line 3-3 in FIG. 2. FIGS. 4A and 4B show static pressure distributions on the suction surfaces (back surfaces) of the respective stator vanes 23 corresponding to views taken along the arrows 4A and 4B in FIGS. 3A and 3B. FIGS. 3A and 3B and FIGS. 4A and 4B show that darker color portions (densely shaded portions) exhibit higher pressures and lighter color portions (coarsely shaded portions) exhibit lower pressures.

According to the embodiment, the first and second recessed portions 32, 33 are formed in the inner peripheral surface of the outer portion 17A of the fan casing 17 to which the tip-side end portion 23 d of the stator vane 23 is connected. Thus, the flow rate of the air flow flowing along the first and second recessed portions 32, 33 is lowered, and thereby the static pressure is raised.

As is clear with reference to Comparative Example and the embodiment in FIG. 3A to FIG. 5B, it is proved that, due to an effect of the first recessed portion 32 of the fan casing 17, the static pressure of the pressure surface of each of the stator vanes 23 in the embodiment is raised in comparison with Comparative Example (see FIGS. 3A and 3B). Furthermore, it is proved that, due to an effect of the second recessed portion 33 of the fan casing 17, the static pressure rearwardly of the rear edge 23 b of the stator vane 23 in the embodiment is raised in comparison with Comparative Example (see FIGS. 4A and 4B).

In addition, as is clear from FIGS. 4A and 4B, a static pressure contour along the suction surface of the stator vane 23 in the embodiment becomes upright in comparison with Comparative Example due to the effect of the first recessed portion 32 of the fan casing 17. In other words, in the embodiment, the static pressure contour is approximately aligned with the radial direction. In contrast, in Comparative Example, the static pressure contour outward in the radial direction is swept back rearward. Accordingly, a static pressure distribution is formed in which a region (a lower side in the figure) inward in the radial direction, of the static pressure contour, exhibits a higher pressure and a region (an upper side in the figure) outward in the radial direction, of the static pressure contour, exhibits a lower pressure. This induces a secondary flow flowing from the hub-side end portion 23 c to the tip-side end portion 23 d of the stator vane 23. On the other hand, in the embodiment, the static pressure contour has almost no sweepback angle, and thus the secondary flow is hardly induced.

Meanwhile, a rotor hub of the fan rotor 15 located frontwardly of the fan stator 16 has a diameter increased from the front to the rear in such a manner as to have a conical shape. This easily induces the secondary flow in the air flow passing along the stator vane 23 of the fan stator 16, the secondary flow flowing from the inner side in the radial direction to the outer side in the radial direction. Moreover, when the stator vane 23 is swept, the air flow easily flows from the hub side to the tip side, making the secondary flow further stronger. As described above, when the secondary flow flowing from the inner side in the radial direction to the outer side in the radial direction along the stator vane 23 is generated, a low-momentum wake (a following wake) generated on the hub-side end portion 23 c of the stator vane 23 easily spreads outward in the radial direction, as shown in Comparative Example in FIG. 5B. This causes a problem of increased pressure loss in the fan stator 16.

According to the embodiment, however, the static pressure contour along the suction surface of the stator vane 23 becomes upright due to the effect of the first recessed portion 32 of the fan casing 17, so that the secondary flow flowing from the hub side to the tip side is suppressed. In addition, the static pressure rearwardly of the rear edge 23 b of the tip-side end portion 23 d of the stator vane 23 is raised due to the effect of the second recessed portion 33 of the fan casing 17, so that the secondary flow flowing from the hub side to the tip side is suppressed. Thereby, as shown in the embodiment in FIG. 5A, a region where the low-momentum wake spreads is minimized, and thus the pressure loss can be reduced.

FIGS. 6A and 6B show flow lines of the air flow along the suction surface of the stator vane 23. Comparative Example shows that the air flow flowing in from the front edge 23 a along the hub-side end portion 23 c of the stator vane 23 deflects largely outward in the radial direction at the rear edge 23 b to increase a wake region Wh on the hub side, while the embodiment shows that the secondary flow flowing from the hub side to the tip side is suppressed to reduce a wake region Wh on the hub side. Here, the static pressure rearwardly of the rear edge 23 b of the tip-side end portion 23 d of the stator vane 23 is raised due to the effect of the second recessed portion 33 of the fan casing 17, and thereby the secondary flow flowing from the tip side to the hub side is generated, so that a wake region Wt on the tip side in the embodiment is slightly larger than that in Comparative Example. The wake regions, however, are made smaller as a whole, and thereby the pressure loss can be reduced.

FIG. 7 is a graph showing changes of the total pressure loss in changing the mass flow rate. It is proved that in the mass flow rate in an illustrated range, the total pressure loss in the embodiment is approximately 20% lower than the total pressure loss in Comparative Example.

FIG. 8 is a graph showing a distribution of the total pressure loss of the stator vane 23 in a span direction in a case of mass flow rate=1.0. It is proved that due to the increased wake region Wt on the tip side in the embodiment in some region (80% to 90% region in the span direction) on the tip side, the total pressure loss in the embodiment is increased in comparison with Comparative Example. However, the total pressure loss in the embodiment in the other region is lower than the total pressure loss in Comparison Example.

An embodiment of the present invention has been described above, but the present invention is not limited to the aforementioned embodiment, and various design changes can be made without departing from the gist of the present invention.

For example, in the embodiment, the present invention is applied to the fan casing 17 of the turbofan engine E for an aircraft, but is not only applicable to a turbofan engine for any application other than that for an aircraft but also applicable to a casing of an axial-flow compressor for any application.

In addition, although the stator vanes 23 in the embodiment are swept, the present invention is applicable to stator vanes which are not swept. 

1. An inner peripheral surface shape of a casing of an axial-flow compressor, the casing surrounding an outer periphery of vanes of a stator which are disposed in a radial arrangement and rearwardly of a rotor of the axial-flow compressor, wherein a generating line of the casing comprises a recessed region and a protruding region, the recessed region being recessed outward in a radial direction from a position frontwardly of a front edge of each of the vanes to a position rearwardly of a rear edge of the vane, the protruding region bulging inward in the radial direction at an intermediate position of the recessed region in a front-rear direction.
 2. The inner peripheral surface shape of a casing of an axial-flow compressor according to claim 1, wherein the recessed region comprises a first recessed portion on a front side, a second recessed portion on a rear side, a first protruding portion continuous to a front portion of the first recessed portion, a second protruding portion forming said protruding region, and a third protruding portion continuous to a rear portion of the second recessed portion.
 3. The inner peripheral surface shape of a casing of an axial-flow compressor according to claim 2, wherein the first protruding portion, the first recessed portion, the second protruding portion, the second recessed portion, and the third protruding portion are smoothly continuous to each other.
 4. The inner peripheral surface shape of a casing of an axial-flow compressor according to claim 1, wherein each of the vanes is swept so that a tip-side end portion thereof is positioned rearwardly of a hub-side end portion thereof.
 5. The inner peripheral surface shape of a casing of an axial-flow compressor according to claim 2, wherein each of the vanes is swept so that a tip-side end portion thereof is positioned rearwardly of a hub-side end portion thereof.
 6. The inner peripheral surface shape of a casing of an axial-flow compressor according to claim 3, wherein each of the vanes is swept so that a tip-side end portion thereof is positioned rearwardly of a hub-side end portion thereof. 